Scientists
have discovered a tropical forest encased in ash when a volcano erupted
about 300 million years ago. The finding, dubbed the "Permian Pompeii"
after the Roman city that was buried in ash, preserved the forest in a
time capsule:

Palaeoecologists can usually only infer the richness of an ancient
forest ecosystem by piecing together fossils of plant fragments of varying
ages. Only when broad areas are preserved in situ in a geological instant
can researchers get a true picture of the composition and ecology of
the forest, says Hermann Pfefferkorn, a palaeoecologist at the University
of Pennsylvania in Philadelphia. Although floods can cover wide swathes
of landscape with sediment in one fell swoop, they often bring in organisms
from other areas and wash local inhabitants away. The most reliable
preservation, Pfefferkorn suggests, comes from a smothering layer of
volcanic ash.

Pfefferkorn and his colleagues have unearthed one such time capsule
from 298-million-year-old rocks in northern China — a 'forest
Pompeii' where the weight of falling ash ripped leaves from twigs, toppled
trees and then buried the lot. The consistent thickness of ash deposits
in the region, as well as the size of individual ash particles, suggest
that the volcanic blast occurred more than 100 kilometres away.